In the operation of internal combustion engines, the air/fuel mixture flows through the connecting piece from the carburetor to the combustion chamber. A portion of the fuel, especially long-chain hydrocarbons, deposits on the inner wall of the connecting piece and forms a fuel film. An enrichment of the mixture can occur when pivoting the apparatus especially in idle because of fuel which is entrained from the connecting piece. A sudden mixture enrichment can lead to disturbances in the smooth running of the engine up to stalling thereof. This is especially the case for engines having low power-weight ratio.
U.S. Pat. No. 4,711,225 discloses a connecting piece between carburetor and combustion chamber which is made of elastic material and has expansion folds. Knurling is provided in one region of the connecting piece to avoid that fuel deposits on the inner wall of the connecting piece. The knurling is intended to prevent the formation of an uninterrupted fuel film.
It has been shown that the fuel, which deposits in the connecting piece, forms droplets especially in the region of the smooth wall and these droplets only flow to the engine when they have reached a certain size. The internal combustion engine suddenly receives too much fuel because of the droplet formation.